Studies already completed in this project have demonstrated that exposure to UV radiation affects immune responses and components of the immune system. These observations will be expanded and the pathogenesis of this effect of radiation will be explored. The models used to date will continue to be studed, viz: in vitro exposure of lymphocytes to radiation, in vivo exposure of animals and humans. Various functions of lymphocytes are impaired following in vitro exposure to UV radiation. The relative sensitivity of individual subpopulations of normal human lymphocytes will be studied with the aim of increasing our understanding of the changes observed after in vivo exposure of animals and humans. In the guinea pig, certain immune responses are suppressed by exposure to UV radiation. The systemic effect of such exposure on the development of allergic contact dermatitis and the antibody response to an injected antigen will be studied. In humans, whole-body exposure to UVB radiation alters the distribution and certain functions of circulating lymphocytes. The extent of these alterations will be explored further and the mechanism by which they occur will be studied. Some of the beneficial and adverse effects of exposure to UV radiation appear to involve immunologic mechanisms. Increased knowledge concerning the nature and pathogenesis of UV-induced alterations of immunity should therefore lead to a better understanding of these effects.